(1) Field of the Invention
This invention relates to a shielded metal arc welding electrode for Cr-Mo low alloy steels, which is capable of forming a weld with a high notch-toughness along with a low sensitivity to temper embrittling, and more particularly to a covered welding electrode which has Al and N positively added to one or both of its core wire and covering flux to obtain such a weld.
(2) Description of the Prior Art
Cr-Mo low alloy steels such as 1Cr-1/2Mo steel, 11/4Cr-1/2Mo steel, 21/4Cr-1Mo steel, 3Cr-1Mo steel and the like are widely applied industrially as a material of high heat resistance in the fields of boilers of high temperature and pressure, petroleum industry, synthetic chemistry or for uses requiring resistance to hydrogen of high temperature and pressure. Namely, Cr-Mo low alloy steels have been developed with a view to the improvements in high temperature strength and high temperature creep characteristics, so that it has been the general practice to put the utmost importance on the high temperature strength of the deposited metal in determining the weld designs of these materials. Meanwhile, the Cr-Mo low alloy steels have come to be used in severer environments, imposing higher criteria on other characteristics on various occasions. The first point is the improvement in low-temperature notch-toughness to cope with the increased use under cold climate, and the second point is the formation of a deposited metal of low sensitivity to temper embrittling which inevitably occurs, for example, to reactors which are used at high temperatures for a long time period of ten to twenty years.